Powered devices need to have a mechanism to supply power to the operative parts. Typically systems use a physical power cable to transfer energy over a distance. There has been a continuing need for systems that can transmit power efficiently over a distance without physical structures bridging the physical gap.
Systems and methods that supply power without electrical wiring are sometimes referred to as wireless energy transmission (WET). Wireless energy transmission greatly expands the types of applications for electrically powered devices. One such example is the field of implantable medical devices. Implantable medical devices typically require an internal power source able to supply adequate power for the reasonable lifetime of the device or an electrical cable that traverses the skin. Typically an internal power source (e.g., battery) is feasibly for only low power devices like sensors. Likewise, a transcutaneous power cable significantly affects quality of life (QoL), infection risk, and product life, among many drawbacks.
More recently there has been an emphasis on systems that supply power to an implanted device without using transcutaneous wiring. This is sometimes referred to as a Transcutaneous Energy Transfer System (TETS). Frequently energy transfer is accomplished using two magnetically coupled coils set up like a transformer so power is transferred magnetically across the skin. Conventional systems are relatively sensitive to variations in position and alignment of the coils. In order to provide constant and adequate power, the two coils need to be physically close together and well aligned.
Existing systems that transmit power wirelessly based on magnetic fields typically operate either in the near-field only, where the separation of the transmitter and receiver coils is less than the dimension of the coils, or in mid-range, where the separation is comparable to the coil dimensions, but then only with single a transmitter and a single receiver coil. Single-transmitter-coil, single-receiver-coil systems are susceptible to a loss in power transmission if the receiver coil is oriented such that no magnetic fields lines emanating from the transmitter coil passes through the receiver coil, e.g., if a flat receiver coil is oriented with its normal perpendicular to the magnetic field lines.